This document creates additional Session Initiation Protocol (SIP) Resource-Priority namespaces to meet the requirements of the 3GPP-defined Mission Critical Push To Talk (MCPTT) and places these namespaces in the corresponding IANA registry.

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The Third Generation Partnership Project (3GPP) has defined a Mission Critical Push To Talk (MCPTT) over LTE service [TS.3GPP.22.179]. The MCPTT service supports an enhanced Push To Talk (PTT) service that is suitable for mission critical scenarios and is based upon 3GPP Evolved Packet System (EPS) services. The requirements for the MCPTT service defined within 3GPP can also form the basis for other PTT services.

The MCPTT service is intended to support communication between several users (a group call), where each user can gain permission to talk in an arbitrated manner. However, the MCPTT service also supports private calls between pairs of users.

MCPTT is primarily targeted to provide a professional PTT service to, e.g., public safety, transport companies, utilities, and industrial and nuclear plants. In addition to this, a commercial PTT service for non-professional use (e.g., groups of people on holiday) may be delivered through an MCPTT system. Based on their operational model, the performance and MCPTT features in use vary per user organization, where functionality that is more mission-critical-specific (e.g., Imminent Peril Call) might not be available to commercial customers.

The MCPTT service provides its users with different priorities for the access to network resources in order to provide means to prioritize between calls when resources are scarce. Among other things, these priorities take into account the priority and role of the caller, the priority and type of the group, and the situation in which the call is made.

The SIP-level call control procedures using these namespaces are specified in [TS.3GPP.24.379]. The namespaces defined here will support a wide range of queuing options. The namespaces correspond to what can be supported over the 3GPP Rx interface, defined in [TS.3GPP.29.214]. The usage of the namespaces can be tailored to the needs of the operator. The mechanism to do this is to configure which values a specific user is allowed to use. This configuration is specified in [TS.3GPP.24.384].

High-priority calls (when the life of either a public safety worker or anyone else is in danger) need to be set up immediately; thus, they require preemption. Other calls may be less sensitive in call setup time but have a high priority once established. For these calls, a queueing mechanism is more appropriate. The MCPTT data transfer service currently under development can benefit from a queueing mechanism. Another example is video-only calls that are not critical in call setup time but where keeping the call is important.

This document creates additional SIP Resource-Priority namespaces to meet the requirements of the 3GPP-defined MCPTT and places these namespaces in the IANA registry.

This document defines namespaces applicable for MCPTT services defined by 3GPP that use the network services of a 3GPP-defined LTE network. The use of this namespace outside such networks is undefined.